The invention generally relates to the field of Light-Emitting Diode (LED) technology. More specifically, the invention relates to LED packaging and encapsulation.
An LED component essentially comprises an LED chip (a piece of semiconductor material with appropriate wire leads) and a package (typically a substantially transparent material, configured in a dome shape, the dome acting as a lens for the emitted light).
The package must be rigid enough, at least on its exterior, to make the LED component structurally sound. On its interior, however, the package must be soft or resilient enough in the vicinity of the LED chip, that mechanical stresses do not damage the LED chip or the wire leads. Throughout, the transparent material of the package must keep light attenuation as small as possible, and must not adversely affect the spectrum of light which is emitted from the LED component.
Conventionally, it has been necessary to compromise between these different objectives. Materials such as PMMA (polymethylmethacrylate: acrylic or xe2x80x9cplexiglasxe2x80x9d), glass, polycarbonate, optical nylon, transfer molded epoxy, and cast epoxy have been used for encapsulation.
However, these materials suffer from the drawback that their optical transmissive characteristics degrade over time. As the material degrades, light is absorbed (xe2x80x9cattenuationxe2x80x9d) to an increasing degree. In particular, light with shorter wavelengths, from the UV through the yellow, is absorbed. The result is called xe2x80x9cyellowingxe2x80x9d, because the eye perceives the light, tending more toward longer wavelengths, as yellowish.
Note, incidentally, that there is also degradation due to decreased light output from the LED die itself.
Different LED components are configured for particular wavelengths of light. For instance, Red (xe2x89xa7515 nm) and Yellow or Amber (xcx9c580-595 nm) LED technology are well-developed. By contrast, green through blue LEDs (400-570 nm) present design problems which have been more difficult to overcome.
Yellowing of the light-transmissive encapsulant material is not an issue for longer-wavelength Red, Amber, or Yellow LEDs. However, shorter-wavelength LEDs are particularly subject to attenuation because of yellowing.
Therefore, there is a need for an encapsulant for LEDs in the near UV, blue, and green range which avoids the drawbacks associated with yellowing and attenuation of the encapsulant material.
There is provided, in accordance with the invention, an LED component, for light of a wavelength in the green-to-near UV wavelength range, approximately 570 to 350 nm. The light-emitting semiconductor die is encapsulated with one or more silicone compounds, including a hard outer shell, an interior gel or resilient layer, or both. The silicone material is stable over temperature and humidity ranges, and over exposure to ambient UV radiation. As a consequence, the LED component has an advantageously long lifetime, in which it is free of xe2x80x9cyellowingxe2x80x9d attenuation which would reduce the green-to-near UV light output.